A magnetic tape storage systems is an efficient and inexpensive means for providing computer data storage functions such as disk back-up, archival storage, software distribution, data interchange, and real-time data recordation. Digital audio tape (DAT) provides flexible, high performance storage applicable to a wide variety of tasks. However, prior art DAT drives are primarily designed for audio systems and thus do not provide the required performance, reliability, or diagnostics necessary for computer data storage. Prior art DAT systems for computer storage typically use audio mechanisms and electronics with adapter chips to operate with the computer. Computer peripheral application of tape drives requires better data integrity and many more start/stop and high-speed search operations than audio tape drives, which were designed primarily for the continuous play of music or voice. Because of the more strenuous and more stringent requirements of computer data storage, such prior art systems do not provide the required performance and are not sufficiently reliable for such use.
A typical prior art digital audio tape (DAT) system has a read/write head coupled to a read/write amplifier and an interface unit communicating with a host unit, for example a computer. A tape transport control unit communicates with the head amplifier and the interface and with a digital capstan control unit having a power amplifier and a reel servo-control unit serving a supply reel and a take-up reel and their motors. A capstan and pinch roller is positioned between the read/write head and the take-up reel and controls tape speed over the head. Tape speed control is important for the generation of accurate track angles during writing. Controlled stopping is particularly important to avoid overshoot and tape creep. Typical DAT recording speeds of 8.15 mm/s require accelerations of 2 m/s.sup.2 exerting considerable stresses on the tape.
Video recorders and some audio recorders utilize a rotating head for read and write. A typical rotating head-helical scan head is embedded between stationary upper and lower mandrels with the tape helically wrapped around the mandrels. The tape moves at a lower angular velocity than the rotating head to produce helically-written data of very high spatial density because of close track spacing. Addressing the closely-spaced tracks then requires accurate control of the linear positions of the tape around the head unit. By pressurizing the mandrels the tape is hydrostatically supported over the head by an air film at higher tape speeds. Tape speeds may be as high as 40 m/s in rotating head-helical scan systems. At such high data densities and tape speeds, accurate sensing requires precise head and tape speeds control and tape tracking control.